This invention relates to a chiller apparatus, and more particularly to a chiller apparatus for cooling or chilling a load required to be chilled such as a semiconductor manufacturing equipment.
A chiller apparatus which has been conventionally known in the art is generally constructed in such a manner as shown in FIG. 4 by way of example. More specifically, the conventional chiller apparatus includes a cooler or chiller 1 for chilling a refrigerant circulated through a primary circuit 2. The thus-chilled refrigerant of the primary circuit 2 is heat-exchanged with a refrigerant of a load circuit 29, which then chills a load A such as a semiconductor manufacturing equipment.
The primary circuit 2 is provided with a pump P.sub.1 and a primary buffer tank 4, so that the refrigerant of the primary circuit 2 may be circulated as indicated at an arrow 2' in FIG. 4. The load circuit 29 is likewise provided with a pump P.sub.2 and a buffer tank 6, so that the refrigerant of the load circuit 29 chilled through the heat exchanger 3 may be circulated as indicated at an arrow 29'. Arrangement of the buffer tank 6 at the load circuit 29 as well is for the purpose of increasing the refrigerant on a side of the load circuit 29 by an amount corresponding to a volume of the buffer tank 6 to facilitate absorption of a variation in temperature of the load A or an increase in temperature thereof.
A temperature of the load A is feed-backed to the chiller 1 of the primary circuit 2. The chiller 1 is adapted to start operation or be increased in output when a temperature of the load A is increased to a level equal to or above a predetermined level. When the chiller 1 starts high-power operation, chilling is carried out in order of the refrigerant of the primary circuit 2, the refrigerant of the load circuit 29 and the load A.
Now, operation of the thus-constructed conventional chiller equipment carried out when a temperature of the load A is varied will be described with reference to FIGS. 4 and 5, wherein FIG. 5 shows a variation in temperature T.sub.1 of the load A, temperature T.sub.2 of the refrigerant of the load circuit 29 and temperature T.sub.3 of the refrigerant of the primary circuit 2 with respect to time.
In FIG. 5, X.sub.0 indicates a control target temperature of the load A. Initially, the temperature T.sub.1 of the load A, the temperature T.sub.2 of the refrigerant of the load circuit 29 and the temperature T.sub.3 of the refrigerant of the primary circuit 2 are kept equilibrated at the control target temperature X.sub.0. Then, when the temperature T.sub.1 of the load A is rapidly increased at time t.sub.1, the temperature T.sub.2 of the refrigerant of the load circuit 29 is increased correspondingly. Whereas, the load circuit 29 is provided with the buffer tank 6 as described above, resulting in the refrigerant of the load circuit 29 being increased in total amount. This keeps the temperature T.sub.2 of the refrigerant of the load circuit 29 from being increased in a manner similar to the temperature T.sub.1 of the load A.
The temperature T.sub.1 of the load A is then feed-backed to the chiller 1, so that the chiller 1 is increased in power when it detects an increase in temperature T.sub.1 of the load A. An increase in power of the chiller 1 leads to a reduction in temperature T.sub.3 of the refrigerant of the primary circuit 2, resulting in the temperature T.sub.2 of the refrigerant of the load circuit 29 heat-exchanged with the refrigerant of the primary circuit 2 being likewise decreased. Such a reduction in temperature T.sub.2 of the refrigerant of the load circuit 29 leads to a reduction in temperature T.sub.1 of the load A.
Thus, operation of the chiller 1 leads to a reduction in temperature T.sub.3 of the refrigerant of the primary circuit 2, temperature T.sub.2 of the refrigerant of the load circuit 29 and temperature of T.sub.1 of the load A in order. This causes much time to be taken from starting of operation of the chiller 1 to returning of the temperature T.sub.1 of the load A to the target temperature X.sub.0.
In particular, the conventional chiller apparatus is provided with the buffer tank 6 in order to rapidly absorb any temperature variation of the load A, to thereby increase the total amount of refrigerant of the load circuit 29, so that much time is required to decrease the temperature. This causes the apparatus to be deteriorated in responsibility of temperature control with respect to an increased variation in temperature or a large increase in temperature.
Such a deterioration in responsibility of the temperature control causes a failure in control of a temperature of the load A with increased accuracy. However, it is often required to control the load A with increased accuracy. This is required when the load A is, for example, a semiconductor manufacturing apparatus. In particularly, in film formation techniques such as CVD, PVD or the like, it is required to control a temperature of a substrate within a range of .+-.5.degree. C. in order to ensure formation of a uniform film.
However, the conventional chiller apparatus, as described above, is deteriorated in responsibility, to thereby fail to control a temperature of the load A within a range of, for example, .+-.5.degree. C. More specifically, it often carries out temperature control of the load beyond the allowable temperature range. Also, it often causes a failure to permit a temperature of the load A once exceeding the temperature range to be rapidly returned to the allowable temperature range. It is of course that departing of the temperature from the allowable temperature range over a long period of time causes a film formed to be nonuniform in quality.
In order to improve responsibility of the temperature control, it would be considered to carry out full-power operation of the chiller 1 to rapidly decrease a temperature of the refrigerator, to thereby chill the load A. However, in the conventional chiller apparatus, the amount of refrigerant of the load circuit 29 is significantly increased, so that a rapid decrease in temperature of the refrigerant is a burden to the chiller 1. This requires to incorporate a large-sized chiller into the chiller apparatus. Also, an increase in burden to the chiller 1 causes it to be deteriorated in durability. In addition, large-sizing of the chiller 1 leads to further disadvantages such as large-sizing of the whole chiller apparatus, a restriction of a place at which the chiller apparatus is to be installed, an increase in equipment cost and the like.
Also, when the temperature of the refrigerant of each of the primary circuit 2 and load circuit 29 is rapidly reduced, a decrease in temperature of load A is delayed from the decrease in refrigerant temperature. This, when the load temperature T.sub.1 reaches the control target temperature X.sub.0, often causes the temperature T.sub.2 of the refrigerant of the load circuit 29 to be excessively decreased. In this instance, the temperature T.sub.1 of the load is also caused to be decreased below the control target temperature X.sub.0 subsequently to the decrease in temperature T.sub.1. At this time, when the decrease in temperature T.sub.1 exceeds the above-described allowable range of .+-.5.degree. C., a film formed is deteriorated in quality and uniformity.
The load temperature thus excessively decreased may be returned to the appropriate range by either interrupting operation of the chiller 1 or reducing the operation, to thereby increase the temperature.
For example, as shown in FIG. 5, supposing that the temperature T.sub.1 of the load A is rapidly increased at time t.sub.1 when the load is being driven while keeping thermal equilibrium, such an increase in temperature T.sub.1 of the load A is immediately transmitted to the chiller 1. This results in the chiller 1 being increased in power with the increase in temperature. Thus, the temperature T.sub.3 of the refrigerant of the primary circuit 3 is caused to be temporarily decreased, however, it is caused to be kept unvaried at certain time as shown in FIG. 5. This indicates that the chiller 1 has reached a limitation of full power operation thereof.
As described above, the temperature T.sub.2 of the refrigerant of the load circuit 29 fails to be rapidly reduced irrespective of a decrease in temperature T.sub.3 of the refrigerant of the primary circuit 2. Thus, the temperature T.sub.2 of the refrigerant of the load circuit 29 starts to be decreased after the temperature T.sub.3 of the refrigerant of the primary circuit 2 are decreased to a degree. Also, the temperature T.sub.1 of the lead A starts to be decreased in a short period of time after the temperature T2 of starts to be decreased.
In any event, the conventional chiller apparatus causes misregistration in timings at which the temperatures T.sub.1 to T.sub.3 are decreased. More specifically, the temperature T.sub.3 of the refrigerant of the primary circuit 2 is first decreased and then the temperature T.sub.2 of the refrigerant of the load circuit 29 is decreased, followed by decrease in temperature T.sub.1 of the load A.
In addition to such misregistration in timings, the conventional chiller apparatus causes another problem of excessively chilling the load A because the chiller 1 is operated on the basis of the temperature T.sub.1 of the load A. Even when operation of the chiller 1 is suddenly interrupted in the case that the load A is excessively chilled, the conventional chiller apparatus fails to rapidly return the temperature of the load A to the control target temperature because the load circuit 29 is deteriorated in responsibility due to an increase in total amount of the refrigerant.
Further, when the chiller 1 is kept decreased in power in excess of a required period of time, the temperature T.sub.1 of the load A is caused to be excessively increased. In this instance, unless the chiller 1 is considerably accurately operated, convergence of the temperature control is deteriorated as shown in FIG. 5.